Summary/Abstract: Colorectal cancer (CRC) represents 8% of all cancers with over 1,100,000 people living with CRC in the US alone. The American Cancer Society estimates that in 2018 there will be over 140,000 new CRC cases and over 50,000 deaths from this disease in the United States. Approximately 50% of patients with CRC develop liver metastases (CLM) and these patients have the highest mortality. Thermal ablation (TA) is a minimally invasive local therapy used to treat CLM. TA causes coagulation necrosis larger than the target tumor to create at least a 5 mm margin to diminish local tumor progression (LTP) with a highly favorable safety profile and curative potential. Despite technological evolution of TA, LTP rates remain high, ranging from 3% to 60% during follow-up of ablated liver tumors. We have shown that microwave ablation is less affected by the heat sink phenomena than radiofrequency ablation, when treating perivascular CLM; therefore, we will limit this proposal to the use of microwave for thermal ablation to optimize outcomes. The high LTP rates are the main limitation of the widespread use of TA in the treatment of cancer. In prior work, we demonstrated that viable (OXPHOS antibody positive and/or KI-67 positive) tumor within the ablation zone (AZ) after TA, and KRAS mutations, carry significant risk for LTP and effect patient survival. We hypothesize that residual undetected viable tumor and tumor biology are the most likely mechanisms leading to ablation failure and eventual LTP, even in the face of complete ablation with margins, depicted in conventional anatomic imaging. This proposed clinical trial is designed to overcome these mechanisms, optimizing TA as a treatment for CLM through the following three specific aims: AIM 1: Establish real time cytopathologic and fluorescent assessment of the AZ by immediate post TA biopsy; AIM 2: Determine the 18F-FDG uptake level representing viable tumor immediately post TA of CLM; AIM 3: Identify gene signatures that predict response in patients undergoing TA of CLM through a pre-ablation biopsy and genomic analysis of the target CLM. Real-time cytopathologic evaluation of the AZ (guided by 3D-assisted technology and metabolic imaging) immediately after TA, is a novel method that can be used as a prognostic immediate biomarker of outcomes after TA. More importantly, retreatment will be offered to treat identified, visible residual tumor at the same sitting. We also propose a pre-ablation biopsy and next-generation sequencing (that is a standard of care in our institution) of all CLM undergoing TA. A significantly higher risk for LTP for KRAS mutant compared to KRAS wild type CLM has been recently documented by our group and others. Despite these new findings and prior knowledge that molecular characteristics impact outcomes of TA, a prospective genomic analysis is still lacking. Whole-genome analysis is thus proposed to detect unknown genes that may underlie extreme responders (estimated 10% of cohort). Our study is expected to create an ablation practice paradigm change, improving outcomes in the large population of patients with CLM and other cancers treated by TA.